CS Fallback in NextEPC

Rafael Diniz rafael at rhizomatica.org
Thu Jul 11 20:16:41 UTC 2019

Rhizomatica is very much interested in testing such setup with CS voice
fallback for LTE to GSM.

Rafael Diniz

On 7/11/19 1:47 PM, Harald Welte wrote:
> Hi Sukchan,
> On Fri, Jul 12, 2019 at 12:14:51AM +0900, Sukchan Lee wrote:
>> Today I've added CS Fallback and released NextEPC v0.5.0
> Thanks a lot!
>> So, I'd just like to test this part with Osmocom project, but it seems to
>> be a difficult task. The reason is why I have little knowledge about 2G/3G.
>> Nevertheless, I will try to do it
> I advise you to not spend too much time on it until we can provide you
> with a set of configuration and instructions on how to configure this,
> instead of spending a lot of time in trial and error.  I think we can
> save you some time there.
> A good starting point would be to use the nightly builds for Ubuntu or Debian,
> (see https://osmocom.org/projects/cellular-infrastructure/wiki/Nightly_Builds)
> and try to follow the general instructions of https://osmocom.org/projects/cellular-infrastructure/wiki/Osmocom_Network_In_The_Box.  The goal would be to create a network with two phones/IMSIs
> where you can have a 2G-to-2G voice call first.   Only once that works, the
> LTE neighbor cell information and SGs configuration can be added.
> You will need the following parts for a minimal 2G setup:
> * osmo-trx + osmo-bts-trx (if using SDR like B2x0)
> * osmo-bsc (RR)
> * osmo-msc (MM + CC)
> * osmo-hlr
> * osmo-stp (for SS7/SIGTRAN between BSC and MSC)
> * osmo-mgw (for RTP audio streams; one instance can be shared between BSC and MSC)
> All of the above can run on a single machine
>> BTW, I don't know if there is anyone who wants to integrate this big thing.
> For sure we want to, and we also know there are users out there who want to.
>> Even though I'm not sure if this will help, but let me introduce the
>> configuration of the NextEPC.
> Thanks, this is useful.  We'll try to to set this up accordingly, but it may
> take some time.
> Philipp (Cc) has been developing most of the SGs interface on the Osmocom
> side, he can help you (here on this list and by direct e-mail) with any related
> issues.
>> FYI, I also attach the pcap that I run with nextepc simulator as below.
> Thanks, I'd like to ask Philipp to review this and report if it reflects his
> expectations about the SGs interface procedures.
> btw/unrelated: I've been hacking a lot on TTCN-3 tests for the MME, and
> I've managed to get the way into NAS (EMM/ESM) and am getting all the
> way up to a Attach Reject (see attached pcap).  As I'm only simulating
> S1AP and SGsAP so far (and not diameter), it's expected that the attach
> will be rejected.  I guess I'll start with using nextepc-hss first, and
> add diameter support to the tests only in a later step.
> Regards,
> 	Harald

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